A tubular synthetic-resin foil of the type used to make bags is formed by extruding a tubular synthetic-resin strand from an annular mouth of a nozzle. A stabilizer extends centrally from this nozzle and has an open outer end. Cooling air is directed radially inward at the strand as it exits from the nozzle and is also injected into the annular space between the strand and the stabilizer. The cooling air trapped in the strand serves both to expand and cool it, and is aspirated at some longitudinal spacing from the nozzle into the outer end of the stabilizer.
This arrangement is typically oriented vertically with the strand moving up and away from the nozzle. After being expanded by air pressure inside it, the tube is flattened and then is usually cross-welded and perforated or cut into bags.
The stabilizer is typically of circular section and has a closed outer end and perforations at this outer end through which the cooling air is aspirated. Such an arrangement is satisfactory so long as the neck part of the strand, that is the strand before it is radially expanded to the desired size, is relatively short. When, however, high-pressure polyethylenes are being extruded this neck is fairly long, so that it is fairly common for the resin to come into contact with the intake end of the stabilizer tube and become caught, forcing one to shut down the machine and clear the jam.
It has been suggested to avoid this problem by providing along the stream of cooling air flowing along the outside of the strand and spaced from this strand a sleeve which is provided over its length with spaced circularly annular disks which extend into the flow of the outer stream of cooling air. Such a system is only a poor partial solution to the problem in that jams still occur.